Generally, a three-phase electric motor with a brush which is mounted on a vehicle or the like includes a cylindrical yoke having permanent magnets attached to its inner circumference, and an armature wound with an armature coil and rotatably disposed in the yoke. The armature includes an armature core externally fitted and fixed to a rotational shaft. The armature core is provided with a plurality of teeth in a radial direction, and elongated slots are formed between the teeth in an axial direction. A winding is wound around each of the teeth to form a coil of a three-phase (U-phase, V-phase and W-phase) structure.
Coils are in electrical communication with a plurality of segments attached to the rotational shaft, respectively. Each of the segments is adapted to come into slide contact with the brush, and applies a voltage to the segment from the brush to supply a current to each coil. In this instance, the phases of the currents flowing through the coils alternate, so that different magnetic fields are produced from the coils, respectively. The rotational shaft is rotated by magnetic attraction or repulsive force which is generated between the yoke and the magnet. In addition, the segment which comes into slide contact with the brush is sequentially changed by the rotation, and the direction of the current flowing in the coil is converted, that is, rectification is performed, so that the armature is continuously rotated.
One example of the winding structure of each coil according to the related art will be described with reference to FIG. 7.
FIG. 7 is a developed view of an armature 103 according to the related art to illustrate a winding state of a coil 107, in which a segment 104 and teeth 109 are shown. An air gap between the adjacent teeth 109 corresponds to a slot 101. In this instance, each segment 104 and a winding 102 wound around each of the teeth 109 will be described using the designated reference numerals in FIG. 7.
As shown in FIG. 7, the armature 103 of the related art is provided with 6 slots 101 and 6 segments 104. In each of the segments 104, the segments 104 having the same potential are connected via a short circuit line 125. In addition, a capacitor 126 is connected between the adjacent segments 104.
The winding 102 is first wound around an a1 tooth 109 to form an a1 coil 107, for example, in a case where a winding starting end portion 30 starts to wind from an S1 segment 104. In addition, the winding 102, which starts to wind from an S2 segment 104, is wound around a b1 tooth 109 to form a b1 coil 107. Moreover, the winding 102, which starts to wind from an S3 segment 104, is wound around a c1 tooth 109 to form a c1 coil 107. Winding terminating end portions of the a1 coil 107, the b1 coil 107 and the c1 coil 107 are connected to each other to form a central point 200 of a star wiring. The winding 102, which starts to wind from an S4 segment 104, an S5 segment 104 and an S6 segment 104, is wound around an a2 tooth 109, a b2 tooth 109 and a c2 tooth 109. The winding terminating end portions of the coils are connected to each other to form another central point 200 of star wiring.
In the winding structure of the winding 102, two parallel circuits are formed. That is, one circuit is formed by the a1 coil 107, the b1 coil 107 and the c1 coil 107, and simultaneously, another circuit is formed by the a2 coil 107, the b2 coil 107 and the c2 coil 107 (e.g., refer to Patent Document 1).
However, in the above-described related art, in the case where the winding is wound in a three-phase concentrated winding manner, the number of the parallel circuits is two, irrespective of the number of the slots, so that there is a limit in rendering the diameter of the winding thin. For this reason, since it is necessary to render the line diameter of the winding thick, it is difficult to perform the winding task.    Patent Document 1: Japanese Patent Application, First Publication No. 2004-328987